I came across this today, on the banks of a river close to the ocean, in Tasmania, Australia.I instantly thought it was the spine of a dolphin (with a rib still attached). However after looking at various pictures of dolphin skeletons it appears that the (blades?) on the vertebrae are a different shape to dolphin vertebrae (The blades are slightly triangular, while the blades on dolphin vertebrae seem a bit more square).

Can anyone identify this for me? Is it actually dolphin?

As you can see there were a couple of extra ribs, and some other bone I'm not sure of that still has a tendon attached.